Non-cyanide silver plating bath



United States Patent 3,406,107 NON-CYANIDE SILVER PLATING BATH Kurt R.Grebe, Beacon, and John V. Powers, Sheuorock,

N.Y., assignors to International Business Machines Corporation, Armonk,N.Y., a corporation of New York No Drawing. Filed Dec. 7, 1964, Ser. No.416,594 2 Claims. (Cl. 20446) ABSTRACT OF THE DISCLOSURE A non-cyanidesilver plating bath is described. The bath is composed of ammoniumphosphate, sodium phosphate and silver nitrate. Silver films depositedfrom the above bath .are mirror bright, ductile and have excellentadhesive properties with respect to the substrates upon which the filmsare deposited.

This invention relates to the electrodeposition of silver, and moreparticularly to the improved electrodeposits of silver employing solubleor insoluble anodes.

It is very desirable in the art of electroplating silver to avoid theuse of cyanide in such baths. Although cyanide silver plating baths arecommercially feasible, they have the defect of being poisonous and mustbe operated under highly controlled conditions. Attempts have been madeto obtain non-cyanide silver plating baths to avoid employing adangerous or noxious substance in such baths, but such non-cyanidesilver plating baths have been inefiicient to the point of making themof questionable value in a commercial operation.

Consequently, it is an object of this invention to provide a non-cyanidesilver plating bath that is economically feasible in its operation andcompetitive with cyanide silver plating baths.

It is yet another object to obtain a non-cyanide silver plating bathwhich has high speed in its operation, produces a mirror bright silverdeposit, is extremely ductile and has excellent adhesive properties withrespect to a substrate on which said silver is deposited.

It is a further object to provide a non-cyanide silver plating bath thatis exceedingly stable.

A further object is to obtain a non-cyanide plating bath having goodthrowing power and whose cathode efiiciency is approximately 100%.

The foregoing and other objects, features and advan tages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention.

The new bath comprises ammonium phosphate, sodium phosphate, silvernitrate, all dissolved in water. A representative bath would comprise 20grams of ammonium phosphate, 100 grams of sodium phosphate, grams ofsilver nitrate and suflicient water to make 1 liter of the solution. Thebath is maintained at a temperature between 2595 C., should have a pH of8.5 or higher and the current density of the electrodes in the bathshould be -45 ma./sq. inch.

During the passage of current between the cathode and the anode of theelectroplating bath, wherein said anode could either be soluble orinsoluble, the ammonium phosphate is a source of ammonium ions, thelatter serving to complex the silver. Although the representativesolution shows a ratio of ammonium phosphate to silver nitrate of 2: 1,the ratio of ammonium phosphate to silver nitrate can be made as high as10:1 without interferring with the efliciency of the non-cyanide silverplating bath. Moreover, in the example given, the ratio of sodiumphosphate to silver nitrate is 10:1, such ratio can be altered to be ashigh as 40 or 50:1 without interfering with the operation of the platingbath. Since the sodium phosphate is employed to add to the conductivityof the electroplating solution there is a wide variation in the amountof sodium phosphate permitted. Although a temperature range of 25 95 C.is suggested, optimum depositions are obtained at about 35 C.

The non-cyanide silver plating solution described above has been foundto be exceedingly stable wherein long shelf storage has not appreciablyaltered the brightness, nor ductility nor adhesive qualities of thebath. The silver deposits have been found to be in an unstressedcondition and the extremely good throwing power of such plating solutionhas made it highly desirable for plating irregularly shaped objects.

According to this invention there is provided a noncyanide silverplating bath having the following composition:

While the invention has been particularly described with reference to apreferred embodiment thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention.

What is claimed is:

1. A non-cyanide bath for electroplating silver consisting ofessentially of 20100 g./ l. of ammonium phosphate, from -500 g./1. ofsodium phosphate, from 1050 g./l. of silver nitrate, the balance water,said bath having a pH of 8.5 or higher.

2. A low temperature non-cyanide bath for electroplating silverconsisting of:

Ammonium phosphate "grams" 20 Sodium phosphate do 100 Silver nitrate do10 Water liters 51 References Cited UNITED STATES PATENTS 744,17011/1903 Darlay 20446 X 923,864 6/ 1909 Levy 20446 XR 2,504,272 4/1950McCoy 20446 FOREIGN PATENTS 939,007 10/ 1963 Great Britain.

OTHER REFERENCES American Chemical Journal, p. 335, vol. 12, 1890.

HOWARD S. WILLIAMS, Primary Examiner.

G. KAPLAN, Assistant Examiner.

